Method and Arrangement for a Digital Subscriber Line

1. A method for estimating a transfer function at a central office (CO) to be used for performing loop qualification of a digital subscriber line between the CO, and a customer premises (CP) regardless of the topology of the loop to be qualified, the method comprising the steps of: retrieving at the CO a value Z in1 0 of the impedance at the CO side when the end of the line at the CP is short circuited, retrieving at the CO a value Z in1 0 of the impedance at the CO when the end of the line at the CP is open and estimating, using a calculator, the transfer function based on a transmission matrix T expressed by the following equation: T = [ Z in ⁢ ⁢ 1 ∞ ⁢ f s 2 Z in ⁢ ⁢ 1 ∞ - Z in ⁢ ⁢ 1 0 Z in ⁢ ⁢ 1 ∞ ⁢ Z in ⁢ ⁢ 1 0 2 ( Z in ⁢ ⁢ 1 ∞ - Z in ⁢ ⁢ 1 0 ) ⁢ f s 2 f s 2 Z in ⁢ ⁢ 1 ∞ ⁡ ( Z in ⁢ ⁢ 1 ∞ - Z in ⁢ ⁢ 1 0 ) Z in ⁢ ⁢ 1 ∞ ( Z in ⁢ ⁢ 1 ∞ - Z in ⁢ ⁢ 1 0 ) ⁢ f s 2 ] wherein f S is set to 1 under the assumption that an impedance of the ports of the loop are equal to each other such that the loop to be qualified is assumed to be symmetric independently of the symmetric characteristics of the loop to be qualified.

2. The method according to claim 1 , wherein the retrieved value of the impedance at the CO side, when the end of the line at the CP is short circuited, is retrieved by means of a single-ended line testing (SELT) based method.

3. The method according to claim 1 , wherein the retrieved value of the impedance at the CO side, when the end of the line at the CP is open, is retrieved by means of a single-ended line testing (SELT) based method.

4. An arrangement for estimating a transfer function at a central office to be used for performing loop qualification of a digital subscriber line between the central office (CO) and a customer premises (CP) regardless of the topology of the loop to be qualified, the arrangement comprising: retrieving means for retrieving at the CO a value Z in1 0 of the impedance at the CO side when the end of the line at the CP is short circuited, retrieving means for retrieving at the CO a value Z in1 ∞ of the impedance at the CO when the end of the line at the CP is open and a calculator for estimating the transfer function based on a transmission matrix T expressed by the following equation: T = [ Z in ⁢ ⁢ 1 ∞ ⁢ f s 2 Z in ⁢ ⁢ 1 ∞ - Z in ⁢ ⁢ 1 0 Z in ⁢ ⁢ 1 ∞ ⁢ Z in ⁢ ⁢ 1 0 2 ( Z in ⁢ ⁢ 1 ∞ - Z in ⁢ ⁢ 1 0 ) ⁢ f s 2 f s 2 Z in ⁢ ⁢ 1 ∞ ⁡ ( Z in ⁢ ⁢ 1 ∞ - Z in ⁢ ⁢ 1 0 ) Z in ⁢ ⁢ 1 ∞ ( Z in ⁢ ⁢ 1 ∞ - Z in ⁢ ⁢ 1 0 ) ⁢ f s 2 ] wherein f S is set to 1 under the assumption that an impedance of the ports of the loop are equal to each other such that the loop to be qualified is assumed to be symmetric independently of the symmetric characteristics of the loop to be qualified.

5. The arrangement according to claim 4 , wherein the retrieved value of the impedance at the CO side, when the end of the line at the CP is short circuited, is retrieved by means of a single-ended line testing (SELT) based method.

6. The arrangement according to claim 4 wherein the retrieved value of the impedance at the CO side when the end of the line at the CP is open is retrieved by means of a single-ended line testing (SELT) based method.

7. The arrangement according to claim 4 further comprising a controller for controlling an arrangement at the CP side for automatically changing the load impedance at the CP side.

8. The arrangement according to claim 4 further comprising a controller for controlling an arrangement at the CP side for arranging an open line and a short circuited line.